Pneumatic spreader stoker

ABSTRACT

An improved pneumatic spreader stoker is disclosed for delivering a controlled amount of pulverent fuel at a uniform rate over the grate of a combustion furnace. Fuel feeding means uniformly feeds the fuel into the path of gas flow from a high velocity air jet for discharging the fuel into the combustion chamber of the furnace. A pair of opposed, powered rotary dampers are disposed in the path of gas flow ahead of the fuel infeed for evenly and alternately increasing and decreasing the quantity and pressure of gas delivering the fuel to the combustion chamber. A bypass conduit having air flow control means therein bypasses the rotary dampers and allows a minimum of gas flow to the combustion chamber at all times. The fuel feeding means comprises a pair of rotary screw conveyors preferably operated 90* to 180* out of phase with one another and disposed in side-by-side relation for delivering fuel from an infeed end to a discharge end. The flights of each of the screw conveyors are of increased pitch at the discharge end. Discharge openings in the screw housings below the flights of increased pitch of each screw conveyor diverge outwardly toward the discharge end and allow the fuel to flow uniformly by gravity into the path of gas flow for discharge into the combustion chamber of the furnace.

United States Patent Leman 51 June 13, 1972 Marvin J. Leman, Shelton,-Wash.

[52] US. Cl ..302/l9, 110/105, 214/1826, 222/193, 222/413 [51] Int. Cl ..F23k 3/02 [58] Field ofSearch.. ..214/18.26, 21; 110/105;

[56] References Cited UNITED STATES PATENTS 2,178,360 10/1939 Kohout ..214/21 2,602,706 7/1952 Miller et a1. ..302/19 Primary Examiner-Robert G. Sheridan Attorney-Seed, Berry & Dowrey 5 7 ABSTRACT An improved pneumatic spreader stoker is disclosed for delivering a controlled amount of pulverent fuel at a uniform rate over the grate of a combustion furnace. Fuel feeding means uniformly feeds the fuel into the path of gas flow from a high velocity air jet for discharging the fuel into the combustion chamber of the furnace. A pair of opposed, powered rotary dampers are disposed in the path of gas flow ahead of the fuel infeed for evenly and alternately increasing and decreasing the quantity and pressure of gas delivering the fuel to the combustion chamber. A bypass conduit having air flow control means therein bypasses the rotary dampers and allows a minimum of gas flow to the combustion chamber at all times. The fuel feeding means comprises a pair of rotary screw conveyors preferably operated 90 to 180 out of phase with one another and disposed in side-by-side relation for delivering fuel from an infeed end to a discharge end. The flights of each of the screw conveyors are of increased pitch at the discharge end. Discharge openings in the screw housings below the flights of increased pitch of each screw conveyor diverge outwardly toward'the discharge end and allow the fuel to flow uniformly by gravity into the path of gas flow for discharge into the combustion chamber of the furnace.

9 Claims, 4 Drawing Figures PATENTEDJUH 13 m2 SHEET 10F 2 INVENTOR. MARVIN J. LEMAN JFJIGO 1L ATTORNEYS PATENTEDJUH 13 I972 SHEET 2 OF 2 INVENTOR. MARVIN J. LEMAN @EVYUMQ ATTORNEYS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to an improved pneumatic spreader stoker for delivering refuse fuel to a furnace and to an improved feeding mechanism for feeding fuel uniformly to the pneumatic spreader stoker.

2. Prior Art Relating to the Disclosure Solid refuse fuel or industrial waste by-products such as sawdust, bark, bagasse, etc., are a source of fuel for power boilers in the generation of steam for power, heating, industrial processing or other uses. For satisfactory operation of such furnaces it is essential that the fuel be distributed across the grate of the furnace uniformly and at an even rate to reduce furnace pulsation. Typical of fuel feeders for pulverent fuel found in the prior art are those disclosed in U.S. Pat. Nos. 1,340,274; 1,959,864; and 2,392,480. The Detroit Stoker Company, a subsidiary of United Industrial Corporation, manufactures refuse stokers wherein a metering conveyor conveys the fuel either (1) to a power-driven rotor distributor having air jets provided immediately below the discharge opening of the feeder to aid in distributing the light fuel over the grate of the furnace or 2) to an air-swept distributor spout using a single blade rotary air damper in the spout to control the quantity and pressure of air. Riley Stoker Corporation also manufactures a pneumatic refuse fuel distributor where fuel is fed to a distributor tray. An air jet emerging through an aircontrolled damper into a distributor nozzle at the fuel distributor tray blasts the fuel into the furnace. Neither of these commercial systems mentioned are capable of providing a continuous and uniform fuel supply with no slugging or temporary stoppage. The single blade rotary air damper of the Detroit stoker delivers such a rapid pressure change in the air to the combustion chamber of the furnace that unsatisfactory pressure conditions result.

SUMMARY OF THE INVENTION This invention is directed to an improved pneumatic spreader stoker for pulverent refuse fuel used in firing boilers wherein pneumatic means deliver a flow of gas under pressure through a conduit into which is metered the refuse fuel. The fuel is swept into the combustion chamber of the furnace by the gas. A pair of powered, opposed rotary dampers are positioned in the path of gas flow in advance of the point where the fuel is metered into the gas flow. The rotary dampers evenly and alternately increase the quantity and pressure of gas sweeping the fuel into the combustion chamber of the furnace, enabling even control of the pressure conditions in the furnace. Fuel is metered into the gas stream at a uniform rate by one or more rotary screw conveyors having screw flights of increased pitch at the discharge end, the screw flights of increased pitch discharging the fuel through diverging bottom openings in the screw housing where the fuel falls by gravity into the gas stream for discharge into the combustion chamber of the furnace. I

The objects of this invention are (l) to provide an improved pneumatic spreader stoker utilizing a pair of powered, opposed rotary dampers positioned in the path of flow; (2) to provide an improved rotary screw conveyor or plurality of screw conveyors capable of evenly metering pulverent fuels into the gas stream of a pneumatic spreader stoker; and (3) to provide an improved pneumatic spreader which can be utilized by existing commercial systems with relatively minor modifications.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross sectional view of a power boiler fired by a pulverent fuel spread uniformly over the grate by one embodiment of the improve pneumatic spreader stoker of this invention;

FIG. 2 is a top view of a pair of rotary screw conveyors having flights of increased pitch at the discharge end thereof over diverging metering slots in the bottom side of the screw housing;

FIG. 3 is a partial cross-sectional view along section line 3 3 of FIG. 2 illustrating the metering slots and flight of increased pitch; and

FIG. 4 is a vertical cross-sectional view of a portion of the pneumatic spreader conduit showing the pair of powered opposed rotary damper blades and the dampered by-pass conduit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS:

FIG. 1 shows a conventional power boiler 10 for refuse fuels wherein pulverent fuel such as sawdust, bagasse, bark, etc. is evenly distributed over the grate 11 in the combustion chamber of the furnace with a pneumatic spreader stoker. The hot combustion gases from burning of the pulverent fuel are used to heat water or other fluids flowing through the heat exchange tubes 12. One or more pneumatic spreader stokers is used to feed sufficient fuel to the combustion chamber of the furnace. Communicating with an opening in the side of the wall of the furnace is a distributor spout 13 having two inlet openings therein. The upper inlet opening communicates with a gravity chute 14 which delivers the fuel into the spout 13 by gravity. The lower inlet opening communicates with a conduit 15 in which is disposed a pair of powered, opposed rotary damper blades described in detail later. A motor-driven fan 9 connects with the infeed end of conduit 15. A damper 16 is positioned in the path of gas flow through conduit 15 to control the maximum amount of gas delivered through conduit 15 to the powered rotary dampers. The damper 16 may be automatically or manually controlled.

The powered, opposed rotary damper blade unit or pulsator unit is shown in detail in FIG. 4 and is positioned in conduit 15 and in the path of gas flow through conduit 15. The blades 17 and 18 of the damper are secured to shafts 19 and 20 extending through the conduit 15. The respective ends of the shafts 19 and 20 extend through the wall of conduit 15. Intermeshed spur gears (not shown) are attached to the ends of the shafts extending through the wall of the conduit '15 to drive the blades together. One of the shafts is also connected through suitable gear reduction means to power means 21 secured to a base 21a. The dual blades are mounted for rotation between a closed position (shown in solid lines in FIG. 4) and an open position (shown in dotted lines in FIG. 4). When the blades are in closed position, gas flow into distributor spout 13 is at a minimum. In open position gas flow to the distributor spout and the combustion chamber of the furnace is at a maximum. A by-pass conduit 22 communicates with conduit 15 through openings 23 and 24 on each side of the powered rotary damper blades. The by-pass conduit 22 has mounted therein a damper 25 which may be manually or automatically adjusted between a fully closed position or a fully open position to allow a minimum of gas flow to the distributor spout at all times to keep the spout free of fuel.

The fuel blade rotary damper shown in FIG. 4 provides an even increase and decrease in gas flow as the dual blades rotate between a fully closed position to a fully open position and then to a fully closed position and so forth. The quantity and pressure of gas increases and decreases substantially linearly as contrasted with a single blade rotary damper wherein pressure increase and decrease is quite sudden. The gas pressure needed to distribute the fuel over the grates in the furnace may be adjusted as desired. Generally, the maximum gas pressure is adjusted to distribute fuel across the full length of the grate in the furnace. The maximum gas pressure is adjusted by adjustment of damper 16. The minimum gas pressure supplied to the distributor spout and combustion chamber is controlled by adjustment of damper 25 in the bypass conduit 22. The minimum gas pressure is generally adjusted to keep the distributor spout swept free of fuel at all times. The number of cycles of the dual blade rotary damper per minute may be adjusted as desired. Generally, the number flow through the distributor spout at a uniform and controlled rate. Refuse feel such as bark, sawdust, bagasse, and other such cellulose fuels are generally fibrous, spongy, and have a high moisture content, causing agglomeration, clogging of moving parts of a mechanical device, or formation of chunks. This results in uneven feeding of the fuel to the combustion chamber of the furnace.

Rotary screw feedersof the conventional type have been used to feed refusefuel into a gravity chute and distributor nozzle. for pneumatic blasting into the combustion chamber of a furnace. However a conventional screw conveyor tends to compress the fuel as it moves from the infeed end of the screw to'the discharge end thereof. At the discharge end of the screw the fuel a tendency to drop from the screw in chunks. These chunks of fuel, if blown into the furnace by the air jet, cause rapid pressure variations in thefurnace with resulting unstable and unsatisfactory furnace conditions.

' By increasing the pitch of the flights'of one or more rotary screw conveyors at thedischarge end thereof and by metering the fuel through divergingmetering slots in the bottom side of I the screw housing uniform fuel feed can be accomplished. In-

creasing the pitch of the screw flights of the rotary screw conveyorloosens the fuel compressed during travel through the screw from the infeed end. Metering slots which diverge outwardly at thedischarge end of the screw conveyor directly beneath the flights .of increased pitch also contribute to the breaking up of fuel so as to allow it to flow evenly down the gravity chute into the path of gas flow through the spreader v stoker. Generally'a V-shaped slot is used as shown in FIG. '2;

however, slots of other configurations which diverge outwardly toward the discharge end of the screw conveyor may be used. a

, Twin screws may be used, the screws disposed in side-byside relation. It is preferable to drive the screws 90 to 180 out of phase with each other although they may be driven in phase. Driving the rotary screw conveyors 90 to 180 out of phase aids in evening out the flow of fuel into the gravity chute.

Referring to'FIG. 2 and FIG. 3, screw housings 30 and 31 are mounted within frame 32. Rotary screws 33 and 34 mounted on respective shafts 35 and 36-are mounted in the screw, housings 30 and'3l in a conventional manner. The rotary screws, on'their upper side, communicate with a storage bin 37. The rotary screws are preferably of variable diameter,

the diameter increasing from the infeed end to the-discharge end. The pitch of the flights 38 is increased at the discharge end as shown in FIG. 2. Directly beneath the flights 38 of increased pitch of each rotary screw are discharge slots 39 and 40 diverging outwardly toward the discharge end of the rotary screws.

The shafts 35 and 36, on which are mounted the screw flights, extend through the screw housing and have secured to the end thereof spur gears 41 and 42 which are intermeshed.

The shaft of one of the conveyors connects with suitable power means 43. As mentioned the screws are preferably driven 90 to 180 out of phase with each other.

The combination of the diverging metering slots positioned below the flights of; increased pitch of the rotary screw conveyors provides a uniform flow of fuel through the gravity chute into the stream of the pneumatic stoker unit. The multi-blade, opposed blade rotary damper disposed in the path of gas flow the pneumatic spreader stoker distributes the fuel across the grates in the furnace at a rate of pulsating change to provide ample time for a conventional automatic control system of the furnace to follow furnace conditions.

the rate at which fuel is metered into the pneumatic spreader stoker may be controlled as desired by speeding up or slowing down the rotary screw conveyors. Likewise, gas

flow rate through the pneumatic spreader stoker can'be adjusted as desired, either manually or automatically.

The embodiments of the invention in which a particular property or privilege is claimed are defined as follows:

1. A pneumatic spreader stoker for feeding a controlled,

continuous supply of pulverent refuse fuel to a combustion chamber of a furnace at a uniform rate comprising; i

pneumatic means delivering a flow of gas under pressure through a conduit communicating with the combustion chamber of a furnace, the gas flow capable of discharging the a combustion 2. A pneumatic spreader stoker for feeding a controlled continuous supply of pulverent refuse fuel to the combustion chamber of a furnace at a uniform rate comprising;

a rotary screw conveyor and housing therefor for delivering the fuel from an infeed end to a discharge end, the screw flights of the conveyor being of increased pitch at the discharge end;

a discharge opening in the screw housing below the screw flights of increased pitch, the opening diverging outwardly toward the discharge endof the screw conveyor;

pneumatic means positioned below the discharge opening in the screw housing delivering a flow of under pressure for discharging the fuel passing through the discharge opening into the combustion chamber of the furnace,

a pair of opposed, rotary damper blades disposed in the path of gas flow ahead of the fuel discharge into the gas stream for alternately increasing and decreasing the quantity and pressure of gas available for delivering fuel into the combustion chamber of the furnace at a substantially linear rate, and I means powering the rotary damper blades.

3. The pneumatic spreader stoker of claim 2 including a damper positioned in the path of gas flow ahead of the opposed rotary damper blades for controlling the maximum gas flow to the combustion chamber of the furnace.

4. The pneumatic spreader stoker of claim 3 including a gas conduit means by passing the opposed rotary damper blades and a damper positioned in the path of gas flow through theby-pass conduit, the damper adjustable for' controlling the minimum gas flow to the combustion chamber.

5. The pneumatic spreader stoker of claim 1 wherein the rotary screw conveyor comprises a pair of rotary screw conveyors disposed in side-by-side relation for delivering fuel from an infeed end'to a discharge end, the screw flights of each rotary screw being of increased pitch at the discharge 6. A pneumatic spreader stoker for feeding a controlled.

continuous supply of pulverent refusefuel to the combustionv chamber of a furnace at a uniform rate comprising; a pair of rotary screw conveyors disposed in side-by-sid relation for delivering fuel from the infeed end to a discharge end, the screw flights of each of the conveyors being of increased pitch at the discharge end, a screw housing for the pair of rotary screw conveyors, discharge openings in the bottom of the screw housing below the screw flights of increased pitch of each rotary screw conveyor, each of the discharge openings diverging outwardly toward the discharge end of the rotary screw conveyors,

means for operating the rotary screw conveyors,

means to supply fuel to the infeed end of the pair of rotary screw conveyors,

an air conduit positioned below the discharge openings in the screw housing,

a gravity chute interconnecting the discharge openings in the screw housing with an opening in the conduit for conveying the fuel discharged through the discharge openings into the conduit,

pneumatic means delivering a flow of air under pressure through the conduit for discharging the fuel delivered by gravity through the gravity chute uniformly over the grates in the combustion chamber of a furnace,

a pair of opposed rotary damper blades disposed in the conduit ahead of the opening for fuel flow into the conduit, the dampers rotating from a vertically aligned position wherein air flow through the conduit is at a minimum to a horizontal position wherein the blades of the damper are substantially parallel with each other and wherein air flow therethrough is at a maximum, thereby alternately increasing and decreasing the quantity and pressure of air available for distributing the fuel into the combustion chamber of the furnace,

a by-pass conduit by-passing the opposed rotary damper blades allowing air flow around the opposed blades,

a damper positioned in the path of the air flow through the by-pass for controlling the air flow therethrough, the damper set to deliver a minimum of air flow to the combustion chamber at all times.

7. The pneumatic spreader stoker of claim 6 including a damper positioned in the path of air flow ahead of the opposed rotary damper blades for controlling the maximum air flow to the combustion chamber.

8. The pneumatic spreader stoker of claim 6 wherein the discharge openings in the screw housing are V-shaped slots.

9. The pneumatic spreader stoker of claim 6 wherein the rotary screw conveyors are operated to out of phase with each other. 

1. A pneumatic spreader stoker for feeding a controlled, continuous supply of pulverent refuse fuel to a combustion chamber of a furnace at a uniform rate comprising; pneumatic means delivering a flow of gas under pressure through a conduit communicating with the combustion chamber of a furnace, the gas flow capable of discharging fuel delivered into the gas stream into the combustion chamber of the furnace, feeding means for delivering the fuel at a uniform rate into the flow of gas through the conduit, a pair of opposed rotary damper blades disposed in the path of gas flow ahead of the fuel discharge into the gas stream for alternately increasing and decreasing the quantity and pressure of gas delivered to the combustion chamber at a substantially linear rate; and means powering the rotary damper blades.
 2. A pneumatic spreader stoker for feeding a controlled continuous supply of pulverent refuse fuel to the combustion chamber of a furnace at a uniform rate comprising; a rotary screw conveyor and housing therefor for delivering the fuel from an infeed end to a discharge end, the screw flights of the conveyor being of increased pitch at the discharge end; a discharge opening in the screw housing below the screw flights of increased pitch, the opening diverging outwardly toward the discharge end of the screw conveyor; pneumatic means positioned below the discharge opening in the screw housing delivering a flow of gas under pressure for discharging the fuel passing through the discharge opening into the combustion chamber of the furnace, a pair of opposed, rotary damper blades disposed in the path of gas flow ahead of the fuel discharge into tHe gas stream for alternately increasing and decreasing the quantity and pressure of gas available for delivering fuel into the combustion chamber of the furnace at a substantially linear rate, and means powering the rotary damper blades.
 3. The pneumatic spreader stoker of claim 2 including a damper positioned in the path of gas flow ahead of the opposed rotary damper blades for controlling the maximum gas flow to the combustion chamber of the furnace.
 4. The pneumatic spreader stoker of claim 3 including a gas conduit means by passing the opposed rotary damper blades and a damper positioned in the path of gas flow through the by-pass conduit, the damper adjustable for controlling the minimum gas flow to the combustion chamber.
 5. The pneumatic spreader stoker of claim 1 wherein the rotary screw conveyor comprises a pair of rotary screw conveyors disposed in side-by-side relation for delivering fuel from an infeed end to a discharge end, the screw flights of each rotary screw being of increased pitch at the discharge end a screw housing for the pair of rotary screw conveyors, means for operating the rotary screw conveyors, discharge openings in the screw housing below the screw flights of increased pitch of each rotary screw, each of the openings diverging autwardly toward the discharge end of the rotary screws.
 6. A pneumatic spreader stoker for feeding a controlled continuous supply of pulverent refuse fuel to the combustion chamber of a furnace at a uniform rate comprising; a pair of rotary screw conveyors disposed in side-by-side relation for delivering fuel from the infeed end to a discharge end, the screw flights of each of the conveyors being of increased pitch at the discharge end, a screw housing for the pair of rotary screw conveyors, discharge openings in the bottom of the screw housing below the screw flights of increased pitch of each rotary screw conveyor, each of the discharge openings diverging outwardly toward the discharge end of the rotary screw conveyors, means for operating the rotary screw conveyors, means to supply fuel to the infeed end of the pair of rotary screw conveyors, an air conduit positioned below the discharge openings in the screw housing, a gravity chute interconnecting the discharge openings in the screw housing with an opening in the conduit for conveying the fuel discharged through the discharge openings into the conduit, pneumatic means delivering a flow of air under pressure through the conduit for discharging the fuel delivered by gravity through the gravity chute uniformly over the grates in the combustion chamber of a furnace, a pair of opposed rotary damper blades disposed in the conduit ahead of the opening for fuel flow into the conduit, the dampers rotating from a vertically aligned position wherein air flow through the conduit is at a minimum to a horizontal position wherein the blades of the damper are substantially parallel with each other and wherein air flow therethrough is at a maximum, thereby alternately increasing and decreasing the quantity and pressure of air available for distributing the fuel into the combustion chamber of the furnace, a by-pass conduit by-passing the opposed rotary damper blades allowing air flow around the opposed blades, a damper positioned in the path of the air flow through the by-pass for controlling the air flow therethrough, the damper set to deliver a minimum of air flow to the combustion chamber at all times.
 7. The pneumatic spreader stoker of claim 6 including a damper positioned in the path of air flow ahead of the opposed rotary damper blades for controlling the maximum air flow to the combustion chamber.
 8. The pneumatic spreader stoker of claim 6 wherein the discharge openings in the screw housing are V-shaped slots.
 9. The pneumatic spreader stoker of claim 6 wherein the rotary screw conveyors are operated 90* to 180* out of phase with each other. 